Microorganisms play important roles in our lives. Of primary interest are those microorganisms that cause diseases under a variety of circumstances. Other issues include the economic aspects associated with microbial contamination, such as food spoilage, plant infections, and surface damage. This introductory chapter of Antisepsis, Disinfection, and Sterilization provides a brief description of the various types of target microorganisms, as well as a discussion of some key considerations for biocidal applications, including the evaluation of efficacy, formulation effects, and the importance of cleaning. It offers brief insights of the topics discussed in each chapter in the book. A section presents definitions of the biocidal applications consistent with international consensus documents.

Typical fungal structures. (A) Filamentous fungus (mold). Hyphae are shown as long lines of unseparated cells, with the development of a fruiting body with attached spores. (B) Typical unicellular fungal (yeast) cells. The cells are generally polymorphic. In one case, a budding cell is shown.

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FIGURE 1.2

Typical fungal structures. (A) Filamentous fungus (mold). Hyphae are shown as long lines of unseparated cells, with the development of a fruiting body with attached spores. (B) Typical unicellular fungal (yeast) cells. The cells are generally polymorphic. In one case, a budding cell is shown.

Simplified fungal cell envelope. The cross-linked cell wall is linked to the cell membrane. The cell wall usually consists of innermost fibrils of chitin or cellulose, with outer layers of amorphous, cross-linked glucans.

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FIGURE 1.3

Simplified fungal cell envelope. The cross-linked cell wall is linked to the cell membrane. The cell wall usually consists of innermost fibrils of chitin or cellulose, with outer layers of amorphous, cross-linked glucans.

Bacterial cell wall structures. The cell membranes are similar structures in all types. grampositive bacteria have a large peptidoglycan layer (shown as crossed lines) with associated polysaccharides and proteins. gramnegative bacteria have a smaller peptidoglycan layer linked to an outer membrane. The mycobacterial cell has a series of covalently linked layers, including the peptidoglycan-, arabinogalactan-, and mycolic acid-containing sections.

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FIGURE 1.7

Bacterial cell wall structures. The cell membranes are similar structures in all types. grampositive bacteria have a large peptidoglycan layer (shown as crossed lines) with associated polysaccharides and proteins. gramnegative bacteria have a smaller peptidoglycan layer linked to an outer membrane. The mycobacterial cell has a series of covalently linked layers, including the peptidoglycan-, arabinogalactan-, and mycolic acid-containing sections.

Basic structure of peptidoglycan. Polysaccharides of repeating sugars are cross-linked by peptide bridges. Two different types of peptide bridges, which have been described in grampositive and gramnegative bacterial cell walls, are shown.

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FIGURE 1.8

Basic structure of peptidoglycan. Polysaccharides of repeating sugars are cross-linked by peptide bridges. Two different types of peptide bridges, which have been described in grampositive and gramnegative bacterial cell walls, are shown.

Typical viral life cycle. The stages include (1) attachment, (2) penetration into the cell, and (3) multiplication. Depending on the virus type, viral particles can be released by cell lysis (4a) or by budding (4b); alternatively, the virus can remain dormant in the cell (4c).

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FIGURE 1.11

Typical viral life cycle. The stages include (1) attachment, (2) penetration into the cell, and (3) multiplication. Depending on the virus type, viral particles can be released by cell lysis (4a) or by budding (4b); alternatively, the virus can remain dormant in the cell (4c).

The general structure of lipopolysaccharide. The lipid A component is integrated into the outer membrane of the gramnegative cell wall, with the polysaccharide portion extending to the outside of the cell.

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FIGURE 1.15

The general structure of lipopolysaccharide. The lipid A component is integrated into the outer membrane of the gramnegative cell wall, with the polysaccharide portion extending to the outside of the cell.

Typical time kill, or D-value, determination. A known concentration of the test culture is exposed to the biocide, samples are withdrawn at various times and neutralized, and the population of survivors is determined by incubation on growth medium. The actual exposure can be conducted at various temperatures, in the presence or absence of test soils, or under other test conditions.

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FIGURE 1.18

Typical time kill, or D-value, determination. A known concentration of the test culture is exposed to the biocide, samples are withdrawn at various times and neutralized, and the population of survivors is determined by incubation on growth medium. The actual exposure can be conducted at various temperatures, in the presence or absence of test soils, or under other test conditions.

Rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 106 is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over contact time or dose using a combination of direct-enumeration and fraction-negative methods (solid lines). In process A, “tailing” is observed, which may not allow the extrapolation of the kill curve to a defined probability of survival (known as an SAL). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10–6.

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FIGURE 1.25

Rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 106 is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over contact time or dose using a combination of direct-enumeration and fraction-negative methods (solid lines). In process A, “tailing” is observed, which may not allow the extrapolation of the kill curve to a defined probability of survival (known as an SAL). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10–6.

2. American National Standards Institute.2000.Sterilization of Health Care Products—General Requirements for Characterization of a Sterilizing Agent and the Development, Validation and Routine Control of a Sterilization Process for Medical Devices.ISO 14937:2000.American National Standards Institute,Washington, D.C.